Tide compensation system

ABSTRACT

A method for automatically adjusting the ballast of the floating structure to compensate for changes in tide. This is accomplished by measuring the tide level with a float gauge to obtain a digital signal and also measuring the water level in a ballast tank in the floating structure with a float gauge to obtain a second digital signal. The two signals are electronically compared and by using the difference from these digital signals beyond a preselected value, valves in the ballast tank are actuated to permit entrance of or to expel water from the tank.

i United States Patent 1191 Fromnick et al. [4 Nov. 4, 1975 TIDE COMPENSATION SYSTEM 3,521,593 7/1970 Pangalila 114/125 3,689,953 9/1972 Markakis; 114/125 X [75] Inventors- Fmmmck w'lmmgmni 3,736,898 6/1973 Yamura 114/125 x Del.; Ronald E. Jones, Tulsa, Okla; Robert Mayer Ardmore Primary Examiner-Trygve M. Blix [73] Assignee: Sun Oil Company of Pennsylvania, Assistant Examiner-Stephen G. Kunin Philadelphia, Pa. Attorney, Agent, or FirmG. L. Church; D. R. 22 Filed: Aug. 29, 1974 21 Appl. No.: 501,586 57 ABSTRACT A method for automatically adjusting the ballast of the 52 vs. C]. 114/125; 61/65; 114/45; floating structure to compensate for changes in tide- 114/74 R; 214/14 This is accomplished by measuring the tide level with 51 Int. 01. B63B 39/03 a float gauge to Obtain a digital Signal and also [58] Field 61 Search 61/20, '64, 65; 73/178 R, suring the water level in a ballast tank in the fl g BIAS SETTING LINE RECEIVERS LATCHES W ml GRAY T0 ace 1, ARITHMETIC THUMBWH EEL SWITCH structure with a'float gauge to obtain a second digital signal. The two signals are electronically compared and by using the difference from these digital signals beyond a preselected value, valves in the ballast tank are actuated to permit entrance of or to expel water from the tank.

7'Claims, 4 Drawing Figures BALLAST TANK LINE LATCHES GRAY TO BCD RECEIVERS IQLLQLIQLL em (ROM) TLELQLEJ; W

MPH-Y w SET P DISPLAY D SPLAY 11%, was

US. Patent -Nov. 4, 1975 Sheet 1 of2 3,916,811

MOD O 262.

US. Patent Nov. 4, 1975 Sheet 2 of 2 3,916,811

MJOKFZOU m mJJONE-ZOU HUME QUE

O. EO ll mwIUlr J HUB ozomv mokuzwo zoiuza.

HUD

NOE

*(JQ m5 Ju mJ MOI.

HRH

QUm O.. EO

ETIIIV muIUP J mmuzwUwd m2] TIDE COMPENSATION SYSTEM This invention deals with a system to automatically compensate for changes in tide which would have an effect on a floating structure such as a barge, a floating drydock or the like during the placement of heavy loads on the floating structure. For example, a floating drydock may be positioned adjacent a pier where it is I desired to place a large, heavy section of a ship on the drydock. Placement of such ship section will take considerable time and the rise or fall of the tide which occurs during placement of the section needs to be compensated for as the ship section is maneuvered laterally onto the drydock surface. While this compensation could be done by manual operation of ballast tanks, it is more desirable that the compensation for tide changes be accomplished automatically so that the operators involved with manually controlling the water levels in the ballast tanks to compensate for loading need not be further concerned with the complexities of tide changes.

It is known in the art to adjust floating structures to compensate for level and orientation changes by varying the buoyant forces acting on appropriate positions of the structure. Thus, in US. Pat. No. 3,689,953 it is shown how a floating body such as floating bridges, vessels and aviation landing decks may be stabilized against wind, waves, and tides by a combination of means mounted in the body at selected loci for varying the buoyant forces acting on the selected loci, means responsive to displacements of the floating body relative to the predetermined orientation for actuating the -means for varying the buoyant forces whereby the buoyant forces are varied at selected loci to produce counteracting forces tending to return the floating body to the predetermined orientation and actuating means including means for sensing displacements of the floating body relative to the predetermined orientation. The actual technique employed by the method of this patent involves a sensing and pneumatic system involving a weight responsive platform and a compressed air actuated piston system to effect displacement of the floating body. The method of subject invention is significantly improved over the prior art in that it employs entirely electronic sensing means which are inexpensive, efficient and reliable and accomplishes displacement of the floating body as required by differential ballast means which are also readily built, easily maintained and entirely reliable.

The system of the present invention may be installed in a barge, floating'drydock or other floating structure and automatically controls the ballast in tide ballast tanks on board the floating structure to take on or unload water as the tide changes the position of the floating structure relative to the land elevation. In general this is accomplished by measuring the tide at any time and comparing it to the level of water which is in the tide tanks of the floating structure, and digital, electronic signals are employed to open or close specific valves as required to allow water to flood the tide tanks or to remove water from them. The system of the invention permits a high degree of control and enables the elevation of the drydock with respect to the land to be held to within 0.5 inch during changes in tide varying from to 16 feet. In its broad embodiment the system will compensate for the rise and fall of tide to eliminate tide induced variations in the verticle elevation of a floating structure by a. measuring the tide level to obtain a digital signal, b. measuring the water level in a ballast tank in said floating structure to obtain a digital signal, said ballast tank containing water inlet and outlet means controlled by valves, c. electronically comparing said digital signals, and d. using the difference from said digital signals beyond a preselected value to actuate said valves in said ballast tank to permit entrance of or to expel water from said tank.

As indicated, the invention will be useful with any floating structure, but in a preferred embodiment of the invention it will be employed with a floating drydock and will be so illustrated herein. Furthermore, it will be understood that the invention will preferably be operated with a plurality of tide ballast tanks in order to more readily control balance of the floating structure. However, for ease of discussion a single ballast tank will be illustrated.

FIG. 1 is a simplified block diagram of the system of the invention.

FIG. 2 is a more detailed block diagram of the invention.

FIG. 3 is an end view of a U-shaped flotation drydock with which the system of the invention may be used.

FIG. 4 illustrates a ballast system used with the system of the invention.

Reference is now made to FIG. 1 where a simplified block diagram for the system of the invention is set forth. As indicated above, digital signals from a tide gauge are sent to a unit which applies an adjustable bias signal to the tide gauge signals in order to correct therri as needed for mean low tide variations. The output signals of the biased tide gauge signals proceed to a function generator which contains a digital matrix establishing a table of values for the ballast tank level at various biased tide level values. The function generator determines what the level of water in the ballast tank should be and that information is sent on to a controller-unit which also receives a signal in digital form from a tank gauge indicating the actual water level in the ballast tank. The controller compares these inputs and adjusts the appropriate valves to take on or discharge water from the tanks as required.

Reference is now made to FIG. 2 which shows the system in somewhat more detail. The tide gauge is placed ona stillwell on land near the shore and may be of the commercially available types of float gauges such as a tank top reading gauge made by Varec, Inc. of Gardena, Calif. When using such a gauge, a liquid level transmitter will be added to provide parallel code output in Gray code decimal format. It will be understood, of course, that other appropriate means may be used to convert the analog information into a digital format. Other types of gauges may also be used, as for example, a tape type gauge which employs a coded tape passing through a digital sensor to obtain the appropriate signals.

The digital signals from the gauge are taken to a functional board containing integrated circuits which contains in the single unit for each of the bits of information, line receivers, latches, and a Gray to BCD unit. The line receivers may be omitted if the lines are short (e.g., 10 to 20 feet) but will preferably be incorporated in order to utilize lines up to about 1000 feet.

The line receivers will be preferably high impedance input amplifiers employed in a manner to eliminate line noise. These receivers are commercially available and are high input impedance differential amplifiers, usually fed by a line driver through a twisted pair wire and information from the line driver can be transmitted over a few thousand feet. The purpose of the line receiver is to have a low loss due to voltage drop and this is accomplished by having very low currents running in the lines. To keep the currentlow a high impedance amplifier is used and circuitry within the amplifier detects a differential voltage or a change in polarity of the signal. This system also results in reducing noise inputted to the linesince the lines are not referenced to ground and both lineschange exactly the same, thereby keeping their differential voltage exactly equal. Typical commercial receivers useful are the differential line receivers of the 54/74 series TTL type manufactured by Signetics Corporation.- g The latching circuits are conventional locked D-type storage elements. They will be steered flip-flops in which the output Q is always the same as the D input after a clocked transition. The clock inputs of the latching circuits are supplied with 180 out of phase signals from a two phase generator, the second phase of which is employed for control of the valves in the ballast tanks. 1

The Gray output of the latches circuits is converted to Binary Coded Decimal (BCD) which signals are optionally fed to a display unit for the tide level, and t the Arithmetic Unit.

The Arithmetic Unit is a 16 bit unit which adds and subtracts to the tide reading a bias value used as a variable adjustment for mean low tide variation during the year. The bias is adjusted preferably by a thumbwheel switch. Optionally, but preferably, the output of the arithmetic unit called the adjusted tide is displayed as the sum of the tide and bias on a display unit. Means to accomplish the function of the Arithmetic Unit may be selected from conventional and commercially available equipment, (e.g., a microprocessor such as an Intel of the 2000 series) but a convenient means is a unit using four 4-bit (16 bit parallel) arithmetic units such as those made by Signetics Corporation; e.g., a digital 8000 series Schottky 'TTL/MSI such as the 82882 binary coded BCD unit.

The output of the Arithmetic Unit proceeds to the Function Generator which is a digital device consisting of a BCD to binary converter and a set of six read only memories (ROM) organized to give a 767 X 16 point memory. The commerically available BCD to binary converter such as a Signetics or TI unit 74184 arranged to convert a 3 digit BCD input (i.e., the adjusted tide value) to a bit binary number and these are applied as an address to theinternal memory table in order to select the tank'level so that the output of the ROM, which is one 16-bit BCD word, describes in digital form the ballast tank level required for the desired fixed elevationof the drydock. This digital data, called the-setpoint number, may-also be displayed, as shown, if desired.

The digital output from the Function Generator is then inputted to the controller unit which also has an input from the tank gauges mounted in the floating drydock ballast tank 'which preferably, is of the same type as used with the tide gauge already discussed above. It will be understood that although the invention is illustrated with only one ballast tank being controlled, any

4 number of such tanks in the drydock may be controlled by feeding tank gauge signals and Function Generator signals to individual controller units which, in turn, will control the valve systems in the individual tanks.

The controller is used in the system to determine where the tank level is in relation to the preset points (which determine the proper amount of water in the tank) which is a function of the value of tide at any time. The controller unit consists of conventional digital electronics and comprises an addition section, a subtraction section and a comparator section. Two inputs to the controller as described below are used.

One input to the controller is the setpoint number (S) which is the level the tank should be, and the other input is the tank level (i.e., what the tank level actually is). Within the controller four numbers are generated which are based upon the setpoint input. These four numbers are:

1. Setpoint Adjustable Constant (S+AS) 2. Setpoint Adjustable Constant (S-AS) 3. Setpoint +Fixed Constant (S+AS 4. Setpoint Fixed Constant (S-AS AS is a thumbwheel adjustable constant which represents the maximum numerical value above or below the setpoint that the tank value is allowed to be. If the value of the tank level is greater than S-l-AS it is a signal that there is too much water in the tank and therefore the controller actuates the system to position the valves to pump water out until point S (Setpoint) is reached.

If the tank level is below SAS then there is not enough water in the tank and therefore the Controller tells the system to pump water in until Point S (Setpoint) is reached.

It is preferred to operate so that AS will be a number equal to about 2 inches which means that the tank level is permitted to be only 2 inches above or below the setpoint before the pumping of water into or out of the ballast tank takes place.

This 2 inch variation limits the movement of the dock to less than one-half inch.

In the controller it is possible that in trying to compare the value of the ballast tank digital number representing level S, the unit may overshoot due to the time limitations brought about by the two phase system, and if it does so, it will never see and therefore cannot respond to the numbers. For this reason it is preferred to modify the controller to introduce hysteresis in the system by adding an additional addition and subtraction unit as shown by items 3 and 4 above. These units function to add and subtract another, but smaller constant (A8 to S and thus a range for each value is established which ensures that the comparator will have time to recognize the value somewhere between S AS, and SAS,. Thus this technique allows for more than one number to be equal to a status quo condition. This is desirable in the preferred system in order to insure precise and consistent operation. When a digital number representing the tank level is being compared with S +AS or S AS a search for coincidence is made under a'specific set of conditions for the digits representing those digital numbers and these specific set of conditions will chosen to require the tank level to be equal to or less than (S +AS,) or equal to or greater than (S -AS If one digit is different there will be no coincidence, but by using this preferred technique, the possibility of coincidence is raised by increasing the number of numbers available for coincidence. Such a system thus reduces the chance that a coincidence will be missed during the comparison. When there is coinci-' out water as required for lowering or raising the drydock to compensate for changing load conditions. The drydock will have tide ballast tanks 13 preferably at the corners of the drydock, and these will contain the appropriate equipment (not shown) such as the ballast tank gauge, a circulating pump, valves, input and output ports to compensate for drydock elevation changes due to varying tide levels. A ballast system which may be used in the drydock is illustrated by FIG. 4. As can be seen from the drawing a submersible, centrifugal pump 21 within tank 22 continuously circulates water taken from the body of water in which the drydock is floating through a loop of lines 23 and through open valves 24 and 25 while valves 26 and 29 remain closed. When water is to be taken on to increase ballast, valve 26 is opened and water flows into line 27 through valve 26 and into the tank from nozzle 28 while valves 25 and 29 are kept closed. When water is to be removed from the tank in order to increase the bouyancy of the tank, valves 24 and 26 are in a closed position and valves 25 and 29 are opened so that water in the tank is sucked up through nozzle 30, valve 29, lines 23 and valve 25 to the outside. In the status quo condition; i.e., when no change is required, valves 24 and 25 are open, valves 26 and 29 are closed and thus water circulates through valve 24, line 23, and valve 25. It will be understood that the opening and closing of the valves is controlled by the electronic system (i.e., the signals from the controller discussed above) and conventional equipment means may be used to open and close the valves as required. Preferably, a convential system comprised of a solenoid on a hydraulic system will be used to activate the valves.

The invention claimed is: 1. A method for automatically adjusting the ballast of a floating structure to compensate for changes in tide which comprises a. measuring the tide level to obtain a digital signal, b. measuring the water level in a ballast tank in said floating structure to obtain a digital signal, said ballast tank containing water inlet and outlet means controlled by valves, c. electronically comparing said digital signals d. using the difference from said digital signals beyond a preselected value to actuate said valves in said ballast tank to permit entrance of or to expel.

water from said tank. 2. A method for automatically adjusting the ballast of a floating structure to compensate for changes in tide which comprises a. measuring the tide level with a float gauge to obtain a digital signal, b. measuring the water level in a ballast tank in said floating structure with a float gauge to obtain a digital signal, said ballast tank containing water inlet 6 said ballast tank to permit entrance of or to expel water from said tank.

3. The method of claim 2 where the floating structure is a drydock.

4. A method for autom atically adjusting the ballast of a floating structure to compensate for changes in tide which comprises:

a. measuring the tide level with floating gauge means to obtain a digital signal,

b. measuring the water level in a ballast tank with floating gauge means to obtain a digital signal,

c. employing electronic means comprising a four 4-bit arithmetic unit to add or subtract a variable bias value to the digital output obtained from said tide level gauge means said bias value to compensate for mean low tide variations,

d. employing electronic means comprising a BCD to binary converter and a' 767 X 16 point memory to compare signals obtained from said arithmetic unit with values of ballast tank levels fixed in said memory and defining the desired elevation of said structure,

e. employing electronic means to compare the output of said memory with said digital signal from said gauge in said ballast tank,

f. employing means to add or remove water from said ballast tank, which means are actuated when a preset difference is determined by the electronic means of (e).

5. A floating structure capable of automatic compen sation for changes in tide which comprises in combination with said structure a. means to measure the tide level to obtain a digital signal,

b. means to measure the water level in a ballast tank in said floating structure to obtain a digital signal, said ballast tank containing water inlet and outlet means controlled by valves,

c. means to electronically compare said digital signals (1. means to employ any difference from said compared digital signals beyond a preselected value to actuate said valves in said ballast tank to permit entrance of or to expel water from said tank.

6. The floating structure of claim 5 wherein said structure is a drydock.

7. A floating structure capable of compensating for changes in tide which comprises in combination with said structure:

a. floating gauge means to measure the tide level and obtain a digital signal,

b. floating gauge means to measure the water level in a ballast tank in said floating structure to obtain a digital signal,

0. electronic means comprising a four 4-bit arithmetic unit to add or subtract a variable bias value to the digital output obtained from said tide level gauge means said bias value to compensate for mean low tide variations,

d. electronic means comprising a BCD to binary converter and a 767 X 16 point memory to compare signals obtained from said arithmetic unit with values of ballast tank levels fixed in said memory and defining the desired elevation of said structure,

e. electronic means to compare the output of said memory with said digital signal from said gauge in said ballast tank,

f. means to add or remove water from said ballast tank, which means are actuated when a preset difference is determined by the electronic means of 

1. A method for automatically adjusting the ballast of a floating structure to compensate for changes in tide which comprises a. measuring the tide level to obtain a digital signal, b. measuring the water level in a ballast tank in said floating structure to obtain a digital signal, said ballast tank containing water inlet and outlet means controlled by valves, c. electronically comparing said digital signals d. using the difference from said digital signals beyond a preselected value to actuate said valves in said ballast tank to permit entrance of or to expel water from said tank.
 2. A method for automatically adjusting the ballast of a floating structure to compensate for changes in tide which comprises a. measuring the tide level with a float gauge to obtain a digital signal, b. measuring the water level in a ballast tank in said floating structure with a float gauge to obtain a digital signal, said ballast tank containing water inlet and outlet means controlled by valves, c. electronically comparing said digital signals d. using the difference from said digital signals beyond a preselected value to actuate said valves in said ballast tank to permit entrance of or to expel water from said tank.
 3. The method of claim 2 where the floating structure is a drydock.
 4. A method for automatically adjusting the ballast of a floating structure to compensate for changes in tide which comprises: a. measuring the tide level with floating gauge means to obtain a digital signal, b. measuring the water level in a ballast tank with floating gauge means to obtain a digital signal, c. employing electronic means comprising a four 4-bit arithmetic unit to add or subtract a variable bias value to the digital output obtained from said tide level gauge means said bias value to compensate for mean low tide variations, d. employing electronic means comprising a BCD to binary converter and a 767 X 16 point memory to compare signals obtained from said arithmetic unit with Values of ballast tank levels fixed in said memory and defining the desired elevation of said structure, e. employing electronic means to compare the output of said memory with said digital signal from said gauge in said ballast tank, f. employing means to add or remove water from said ballast tank, which means are actuated when a preset difference is determined by the electronic means of (e).
 5. A floating structure capable of automatic compensation for changes in tide which comprises in combination with said structure a. means to measure the tide level to obtain a digital signal, b. means to measure the water level in a ballast tank in said floating structure to obtain a digital signal, said ballast tank containing water inlet and outlet means controlled by valves, c. means to electronically compare said digital signals d. means to employ any difference from said compared digital signals beyond a preselected value to actuate said valves in said ballast tank to permit entrance of or to expel water from said tank.
 6. The floating structure of claim 5 wherein said structure is a drydock.
 7. A floating structure capable of compensating for changes in tide which comprises in combination with said structure: a. floating gauge means to measure the tide level and obtain a digital signal, b. floating gauge means to measure the water level in a ballast tank in said floating structure to obtain a digital signal, c. electronic means comprising a four 4-bit arithmetic unit to add or subtract a variable bias value to the digital output obtained from said tide level gauge means said bias value to compensate for mean low tide variations, d. electronic means comprising a BCD to binary converter and a 767 X 16 point memory to compare signals obtained from said arithmetic unit with values of ballast tank levels fixed in said memory and defining the desired elevation of said structure, e. electronic means to compare the output of said memory with said digital signal from said gauge in said ballast tank, f. means to add or remove water from said ballast tank, which means are actuated when a preset difference is determined by the electronic means of (e). 